One of the main points of Dan Ariley's book Predictably Irrational was that the chasm between paid and non-paid is so far greater than people usually expect. Even when the transaction is merely pennies, the change in the attitude of a person can be immense. I mean, people have no qualms buying a $600 smartphone, but many of these people would prefer to use a broken ad-filled free app than shell out the whole 99 cents for the paid app. It turns regular joyful activities into work for many people, even if you don't need the income or even don't really care. Basically, even fractions of a cent could cause users to behave significantly different and change the tone of the website. I wouldn't want to see any unintended consequences from such a change.